1. Field of the Invention
This invention generally relates to a method and apparatus for making ice and, in particular, to a method and apparatus for making uniformly sized spherical ice particles.
2. Description of the Prior Art
A mixture of ice particles and cold water may be used as a cold heat transport material in a closed loop cooling system in which the ice particles, which effectively fulfill the thermal transport function of the material, are transported through the cooling system by the water. A drawback of using such a material is that the ice particles, which are typically of nonuniform shape and size, are prone to agglomerate as they pass through the heat exchanger of the cooling system, especially where the diameter of the heat exchanger tubing has been minimized in order to increase the heat transfer efficiency of the exchanger.
Conventional methods for generating ice particles include: indirect-contact methods, in which the ice particles are generated by indirectly contacting the refrigerant with brine; direct-contact methods, in which the ice particles are generated by directly contacting the refrigerant with brine; and vacuum methods.
The conventional indirect-contact ice-making apparatus shown schematically in FIG. 1 comprises: a refrigerant storage container (2), generally an annular cylinder, which has a refrigerant feed port (4) at its top and a refrigerant discharge port (12) at its bottom; a brine flow pipe (8), generally a cylinder coaxial with the annular cylinder, which is enveloped by and in good thermal contact with the refrigerant storage container; an expansion valve (6) which connects a refrigerant source (not shown), generally above the storage container (2), and the refrigerant feed port (4); and a compressor/condenser (not shown), generally below the storage container, which is connected to the discharge port (12).
Refrigerant in the indirect-contact ice-making apparatus described immediately above flows in a closed loop from the refrigerant source through the expansion valve (8), which allows the refrigerant to expand, to the refrigerant storage container (2), and from the refrigerant storage container (2) through the compressor/condenser, which compresses and condenses the refrigerant, back to the refrigerant source. While passing through the brine flow pipe (8), low density brine is cooled by indirect contact with the refrigerant through the walls of the brine flow pipe and is thereby converted into a mixture of high density brine and the ice particles.
The direct-contact ice-making apparatus shown schematically in FIG. 2 comprises: a refrigerant storage container (20), which has a refrigerant feed port (24) at its bottom and a refrigerant discharge port (22) at its top; an expansion valve (26) which connects a refrigerant source (not shown), generally below the storage container, and the refrigerant feed port (24); and a condenser/compressor (not shown), generally above the storage container, which is connected to the discharge port (22).
Refrigerant in the direct-contact ice-making apparatus described immediately above flows in a closed loop from the refrigerant source (not shown) through the expansion valve (26), which allows the refrigerant to expand, into the refrigerant storage container (28), and from the refrigerant storage container (28) through the compressor/condenser (not shown), which compresses and condenses the refrigerant, back to the refrigerant source. While passing through the refrigerant storage container (28), low density brine is cooled by direct contact with the refrigerant and is thereby converted into a mixture of high density brine and ice particles.
In both the indirect-contact and the direct-contact ice-making methods described above, the brine and the ice particles must be separated after ice particles have been formed. Further, both methods typically use refrigerants, such as freon, which adversely affect the environment.
In the vacuum ice-making method illustrated in FIG. 3, ice is formed by filling part of a vacuum chamber with water and then decompressing the vacuum chamber. Since the layer of ice thereby formed at the bottom of the vacuum chamber must be pulverized in order to form ice particles, the vacuum ice-making method does not yield uniformly sized, spherical ice particles.